Reversal of Drug Resistance in a Human Colon Cancer Xenograft Expressing MDR1 Complementary DNA by In Vivo Administration of MRK-16 Monoclonal Antibody

Abstract

One strategy to overcome multidrug resistance in neoplasia is to inhibit the gp170 glycoprotein (relative molecular mass, 170,000) that functions as a plasma membrane, energy-dependent, drug-efflux pump. The human colon cancer cell line HT-29, which grows as an ascitic tumor in athymic NCr-nu/nu nude mice, was made multidrug resistant by infection with an MDR1 (also known as PGY1) retrovirus. Referred to as HT-29mdr1, it was used to study reversal of drug resistance in vivo by the anti-P-glycoprotein monoclonal antibody MRK-16. Flow cytometry and radioimmunoassay demonstrated a marked increase in MRK-16 reactivity on HT-29mdr1 cells as compared with its reactivity on the parental, uninfected cell line (HT-29par). The 50% inhibitory concentrations (IC50) of vincristine on HT-29par and HT-29mdr1 cells were 2.5 and 15 ng/mL, respectively. The MRK-16 monoclonal antibody did not affect the vincristine sensitivity of the HT-29par cells. Pretreatment of HT-29mdr1 cells with 10 micrograms/mL MRK-16 in tissue culture partially restored the vincristine sensitivity (IC50 = 7 ng/mL). This modulation of vincristine sensitivity by MRK-16 was then tested in vivo. The median survival times of mice given intraperitoneal transplants of 5 x 10(6) HT-29par or HT-29mdr1 were 37 and 39 days, respectively. Treatment of mice with 1 mg/kg vincristine weekly for 3 weeks, beginning 10 days after tumor injection, resulted in a significant increase in the median survival time of the HT-29par tumor-bearing mice (68 days, P less than .0001), but it had no effect on the HT-29mdr1 tumor-bearing mice. However, treatment of mice bearing the HT-29mdr1 tumor with MRK-16 before vincristine therapy reversed the resistance to the drug (median survival time = 64 days, P less than .0001). The MRK-16 monoclonal antibody alone had no effect on the median survival time of mice given an injection of either HT-29par or HT-29mdr1 cells. These results suggest that strategies employing monoclonal antibody against gp170 may be clinically useful to reverse multidrug resistance.

Mechanisms of Drug Resistance in Cancer Chemotherapy

“…Another mode of MDR reversal utilises monoclonal antibodies, several of which inhibit P-gp-mediated drug effl ux in vitro [90,91] . For in vivo applications, compa- Various other means of circumventing resistance that are being explored are based on experimental observations described above: these include adjuvant treatment with suramin to reverse fi broblast growth factor-mediated resistance [85] ; inhibition of p13 kinase/Akt to prevent resistance mediated through integrin involvement, and re-expression of wild-type tumour suppressor genes.…”

Efficient inhibition of P-glycoprotein-mediated multidrug resistance with a monoclonal antibody.

“…These investigators found that treatment of some MDR cell lines with a monoclonal antibody (mAb) MRK16 increased intracellular accumulation and cytotoxicity of vincristine and actinomycin D. MRK16 also increased the in vivo toxicity of vincristine to a human MDR cell line grown as a xenograft in nude mice (13). The in vitro potentiation of drug cytotoxicity by MRK16, however, was weak relative to that of chemical inhibitors and was apparently limited to only some of the Pgp substrates, since MRK16 had no effect on doxorubicin cytotoxicity (12).…”

How to overcome ATP-binding cassette drug efflux transporter-mediated drug resistance?

“…Initially, these antibodies were intended to study the membrane changes in MDR cells, but later research demonstrated that MRK-16 was able to inhibit P-gp mediated efflux of vincristine and actinomycin D in vivo [172,173] . The addition of a P-gp inhibitor such as cyclosporine A to MRK-16 treatment, further sensitized MDR myelogenous leukemia cells to vincristine and doxorubicin [174,175] .…”